1. Field of the Invention
This invention relates to a paper shredding machine and, more specifically, to such a paper shredding machine which is capable of cutting the paper into elongated strips while providing a transverse cut to further reduce the size of the resulting pieces of paper. The invention also includes the method of making the cutting discs of such a paper shredding machine.
2. Description of the Prior Art
It is not uncommon in the paper shredding art to provide various types of paper shredders which generally cut or shred the paper into a plurality of elongated strips. Typically, such shredding machines include first and second parallel spaced-apart rotatable shafts. The shafts are driven to rotate in opposite directions. There is included a plurality of cutters or cutting discs having annular cutting surfaces disposed on each shaft and locked against rotation on the shaft by locking means. The adjacent cutters on each shaft are separated by a cutter on the other shaft extending therebetween. Additionally, combers are interposed between the cutters to direct the paper between the shafts and the interfitting cutters thereof and to further direct the resulting strips to a discharge area. The cutting action between the interfitting cutters tends to slice the paper as the side edges of the cutters pass by one another in opposite directions. U.S. Pat. Nos. 2,770,302; 3,630,460; 3,797,765; and 4,018,392 disclose shredding machines of this general type which are well known in the paper shredding art.
There are additional shredding machines in the prior art which include cutting wheels or discs which, although primarily cutting at the side edges thereof, include notches or grooves at the outer surface of the discs. These notches or grooves are primarily intended to grip the paper supplied thereto rather than to produce any transverse cutting of the strips formed by the shredder. U.S. Pat. Nos. 3,033,064; 3,921,920; and 4,194,698 disclose such paper shredders with notched wheels which do not proport to produce any transverse cut of the elongated strip formed by passage of the paper therethrough.
Although the various paper shredders disclosed in the patents mentioned hereinabove have been successfully employed, it has been found that even the production of such narrow, elongated strips does not necessarily satisfy the security requirements of numerous businesses and governmental agencies. Simply reducing the paper to narrow, elongated strips would not necessarily prevent reconstruction of a document shredded in these types of machines. As a result, there remains a need for a paper shredder which is capable of further reducing the size of the resultant pieces for security reasons. Further reducing the size of the elongated strips by introducing a plurality of transverse cuts tends to make reconstruction of an original document almost, if not completely, impossible.
U.S. Pat. Nos. 4,257,565 and 4,565,330 disclose shredding devices which produce longitudinal cuts for the formation of elongated strips and further include transverse notches or teeth which are designed to produce a transverse cut of these elongated strips. However, both of these devices recognize the difficulty of producing any form of notch or tooth in the periphery of such a cutting disc which will, by itself, produce the desired transverse cut. Accordingly, both of these shredding devices include the cutting discs thereof which are aligned to cooperate with combers or spacer members between the cutters on the other for pinching or severing of the paper as the paper passes between the notches or teeth and the end of the comber or spacer member. Basically, these shredding machines include a pair of rotary shafts driven in opposite directions. A plurality of rotary discs are mounted on the rotary shafts and have a plurality of shredding blades or teeth about the outer periphery thereof. A plurality of spacer members, which are aligned with the rotary disc and located between adjacent discs on the opposite shaft, include at least one cutting edge or surface which engages with the shredding blade of the rotary disc so that paper trying to pass through a gap therebetween will be severed or cut.
In an effort to further reduce the size of the resulting pieces of paper produced by a paper shredder, U.S. Pat. No. 3,860,180 discloses apparatus and method for further cutting the strips with a transverse incision which is oblique to the path of the longitudinal strips formed thereby. The shredding machine disclosed therein includes a pair of counter-rotating cutter rollers which include axially-spaced cutter discs having radial side faces and a generally cylindrical periphery outer edge. The cutter discs of each roller fit closely between the cutter discs of the other roller so that the side edges of adjacent pairs of cutter discs form a slitter. There is included means on the circumference of each cutter disc including the trailing edge of at least one generally axially extending notch formed in the outer periphery of the cutting disc to form a transverse interruption in the strips of the document being cut by the adjacent slitters. Each of the notches is inclined from side to side and is displaced circumferentially from the notch in adjacent cutter discs on the same shaft in such a manner that the notches of all of the cutter discs of each roller defines at least one helical groove in the periphery of the respective roller. As a result, the longitudinal strips being formed are further reduced into short sections by making transverse incisions in the document which extends obliquely from the path of one slit to the path of an adjacent slit.
As will be seen, simply providing some form of generally transversely extending notch or tooth to a cutter wheel will not insure that a transverse cut will be produced in the strips formed during the shredding. While the longitudinal strips of paper tend to propagate as the sheets are passing between the cutting discs, propagation in a transverse direction is not as easily produced. In fact, with some configurations, it is not possible to produce a transverse cut in a piece of paper near the ends of longitudinal cuts. Some notch or tooth configurations have been found to simply "push" the paper in such a manner that further propagation of the longitudinal cuts occurs. With further propagation of the longitudinal cuts, the paper would simply move away from the transverse notch or tooth and would not be sufficiently supported to allow a transverse cut to be formed.
On the other hand, it should be recognized that the cutting discs of U.S. Pat. No. 3,860,180 include the notches which are formed at an oblique angle so that the transverse cutting initially occurs at one side of the strip for easier propagation to the other side of the strip. However, formation of the cutting wheels with an obliquely formed notch or tooth therein significantly complicates the manufacturing process of the rollers and the various cutting discs thereof.
As seen in British Pat. No. 2,098,502, a shredding apparatus employing the inclined or oblique notches of the type described in U.S. Pat. No. 3,860,180 further includes additional teeth for proper gripping and support of the paper passing therethrough. Basically, the shredding device disclosed therein includes two driven and intermeshed cutting rollers which are formed by cutting discs which have recesses formed therein. The recesses extend in a generally transverse direction and are formed in the surface of each cutting disc. These recesses, which are not the oblique cutting notches, form an inclined saw-tooth profile which also continues in the adjacent cutter discs in the form of a turned or helical profile in the same manner as the oblique cutting notches. These recesses are intended to grip individual sheets of a stack of paper and further insure proper retention of the paper through the cutter discs in order to produce the longitudinal and transverse cuts thereof.
German Laid Open Patent Appln. No. 32 39 060 Al discloses a series of overlapping cutting discs for a basic longitudinal cut but further includes a complicated series of notches in the surfaces thereof. As generally indicated in the drawings, the notches appear to grip or bend the strip in order to restrict its movement in an effort to allow a toothed area thereof to produce a transverse cut. Whether or not such gripping or bending will properly restrict the movement of the paper, the patent does recognize that the simple introduction of a tooth or notch to the outer edges of a cutting disc will not insure that the paper is transversely cut.
U.S. Pat. No. 3,960,335 and British Pat. No. 2,137,116A disclose additional machines which are purportedly capable of producing transverse cuts to longitudinal strips of sheet material formed therein. The device of U.S. Pat. No. 3,960,335 is primarily directed to cutting sheets of plastic. However, as those skilled in the shredding art must know, any problems experienced in cutting sheets of plastic could be quite different from those associated with cutting paper. Plastic sheets and paper sheets would have quite different propagation characteristics and a device which would cut one might not be capable of similarly cutting the other. Nevertheless, the device disclosed therein includes an elaborate series of teeth which purportedly produce numerous transverse cuts in the sheet plastic prior to the formation of the longitudinal strips as the sheets continue to advance between the side edges of the overlapping discs thereof. On the other hand, one might question the reliability or capabilities of such a configuration when additional embodiments disclosed in U.S. Pat. No. 3,960,335 are directed to the inclusion of a completely different element for producing transverse cuts of the sheet plastic after it has been longitudinally cut to form elongated strips.
Similarly, British Pat. No. 2,137,116A purports to include overlapping cutting discs which have a relatively simple notch therein. This simple notch configuration is said to be able to produce a transverse cut. However, considering the problems associated with producing such a transverse cut in paper material, it is difficult to see how the notch configuration disclosed therein would be any different than the numerous notch configurations which did not produce a transverse cut in the shredding devices which were discussed hereinabove as primarily directed to the formation of simple, elongated strips.
All of the above-mentioned patents are incorporated herein by reference as if the entire contents thereof were fully set forth herein.
Although numerous attempts have been made to provide a simple and efficient shredding machine for cutting paper inserted therein into extremely small pieces, there remains a need for any such machine which is reliable, effective, and inexpensive to provide.